Pneumocystis pneumonia (PCP) is a significant cause of mortality and morbidity in immunocompromised patients. There are limited alternative therapeutic choices to trimethoprim-sulfamethoxazole (TMP-SMX). Antibody responses to surface proteins have been associated with protection from Pneumocystis pneumonia using both active and passive immunization approaches (Zheng et al., J Clin Invest 108:1469-1474, 2001; Zheng et al., J Clin Invest 115:3536-3544, 2005; Empey et al., Infect Immun 72:6211-6220, 2004; Wells et al., Infect Immun 74:2446-2448, 2006; Gigliotti et al., Infect Immun 70:1069-1074, 2002). These data suggest that antibody responses raised against surface epitopes can provide protection against Pneumocystis pneumonia potentially by enhancing opsonic phagocytosis or through activation of complement (Wells et al., Infect Immun 74:390-393, 2006; Steele et al., J Exp Med 198:1677-1688, 2003). A limitation of antigen discovery for this pathogen is the fact that Pneumocystis (Pneumocystis) cannot be cultured in vitro.